Oct.1st, ______is our National Day, is always celebrated with singing and dancig.
The building the windows are bright at night is our school library.
It was not until dark _____ he found _____ he thought was the correct way to solve the problem.
_________ this is the biggest mistake we have made.
It i s the second time that the poor area_______.
In modern times, the development of science is ________ .